Author If Isekai included space travel.
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I enjoyed the read! I particularly love short isekai where the main character doesn't get to do anything in another world.

At first I thought isekai should be strictly for someone traveling to a completely difference world but later on as the amount of isekai light novels increased and the amount of repetition in the genre became excessive the genre morphed a mold for story layouts that include more than just traveling to a different world. So now I believe any story in which someone travels to a different world or goes into a different dimension/time and have more knowledge than the residents of their new environment should be considered isekai.

Following this logic, I believe Murakami Motoka's JIN and Kawaguchi Kaiji's Zipang are loosly isekai as well.